https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111397
Bug ID: 111397
Summary: Spurious warning "'({anonymous})' is used
uninitialized" when calling a __returns_twice__
function (-Wuninitialized -O2)
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: skiminki at gmail dot com
Target Milestone: ---
The following piece of code triggers a spurious warning when calling
test_setjmpex() on GCC 12.3 and GCC 13.2 using -O2 or -O3.
test.c: # compile with: gcc -c -O2 -Wuninitialized test.c
int globalVar = 1;
int __attribute__ ((__returns_twice__)) test_setjmpex(void *context);
void testfn()
{
int localVar = globalVar;
while (!localVar) {
// The below triggers:
// warning: '({anonymous})' is used uninitialized [-Wuninitialized]
test_setjmpex(__builtin_frame_address (0));
if (globalVar)
break;
}
}
No includes needed, so I omitted the .i file. Initially setting
tree-optimization as the component based on a guess.
This was found when compiling Weiss (chess engine) for mingw, but the reduced
test case triggers the warning on regular Linux, too. (Link to the original
issue: https://github.com/TerjeKir/weiss/issues/680 )
Godbolt link: https://godbolt.org/z/ec1dKsx4q
Experimentation with godbolt:
- Affected GCC versions: 12.1 - 12.3; 13.1 - 13.2 ; multiple targets (at least:
x86-64, aarch64, risc-v)
- No warning on 11.x
- No warning on trunk
- No warning on -O1
Full repro:
-----------
# Ubuntu 23.04 / x86_64-linux-gnu
docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp gcc:13.2 gcc -v -c
-O2 -Wuninitialized test.c
Repro output:
-------------
Using built-in specs.
COLLECT_GCC=gcc
Target: x86_64-linux-gnu
Configured with: /usr/src/gcc/configure --build=x86_64-linux-gnu
--disable-multilib --enable-languages=c,c++,fortran,go
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.3.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-c' '-O2' '-Wuninitialized' '-mtune=generic'
'-march=x86-64'
/usr/local/libexec/gcc/x86_64-linux-gnu/12.3.0/cc1 -quiet -v -imultiarch
x86_64-linux-gnu test.c -quiet -dumpbase test.c -dumpbase-ext .c -mtune=generic
-march=x86-64 -O2 -Wuninitialized -version -o /tmp/ccZm0Pke.s
GNU C17 (GCC) version 12.3.0 (x86_64-linux-gnu)
compiled by GNU C version 12.3.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/include
/usr/local/include
/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C17 (GCC) version 12.3.0 (x86_64-linux-gnu)
compiled by GNU C version 12.3.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 1e1b4098557fa4aa478a5470075c20a5
test.c: In function 'testfn':
test.c:12:11: warning: '({anonymous})' is used uninitialized [-Wuninitialized]
12 | test_setjmpex(__builtin_frame_address (0));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
COLLECT_GCC_OPTIONS='-v' '-c' '-O2' '-Wuninitialized' '-mtune=generic'
'-march=x86-64'
as -v --64 -o test.o /tmp/ccZm0Pke.s
GNU assembler version 2.40 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Debian) 2.40
COMPILER_PATH=/usr/local/libexec/gcc/x86_64-linux-gnu/12.3.0/:/usr/local/libexec/gcc/x86_64-linux-gnu/12.3.0/:/usr/local/libexec/gcc/x86_64-linux-gnu/:/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/:/usr/local/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/:/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib64/:/usr/local/lib/gcc/x86_64-linux-gnu/12.3.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-c' '-O2' '-Wuninitialized' '-mtune=generic'
'-march=x86-64'
